I'd like to bet that she was. How many times have you people said that Jeremy taught her ?
This is a perfect example of how you don't pay attention to the actual evidence of the case and thus your opinion of Jeremy's innocence is born entirely on ignorance and bias.
Jeremy lied to police at the scene telling them that he taught her how to operate the Anschutz and that she had fired it and all weapons in the house.
By the time he gave his statement later that day to investigators he changed his story and said he had not known her to have any interest in guns or to have fired any- he made sure to match what the rest of the family was saying. His lies actually would provide an innocent reason for Sheila's fingerprints to be found on the weapon plus it would look suspicious to be the only one with a different story so he dropped the lies.
June told Pam that Jeremy tried to teach Sheila how to load the magazine
but she didn't want to learn. Jeremy wanted her to touch it and the weapon so her prints would be found on it.
That is what people have noted. No one claimed she actually learned how to load and fire the weapon except Jeremy supporters who ignore the evidence and just decide that being around people who own guns is sufficient to result in knowing how to use all of them.